1. Field of the Invention
The present invention relates generally to the field of wireless communication devices and, more particularly, to user equipment supporting at least two frequency bands for communication and a cell search method for the same.
2. Description of the Related Art
Frequency bands used for wireless communication may vary depending upon uses, standards, and systems. For example, Table 1 illustrates some frequency bands used by Global System for Mobile Communications (GSM).
TABLE 1UplinkDownlinkChannelSystemBand(MHz)(MHz)numberGSM-450450450.4-457.6460.4-467.6259-293GSM-850850824.0-849.0869.0-894.0128-251P-GSM-900900890.0-915.0935.0-960.0 1-124E-GSM-900900880.0-915.0925.0-960.0975-1023, 0-124DCS-180018001710.0-1785.01805.0-1880.0512-885PCS-190019001850.0-1910.01930.0-1990.0512-810
Typically, only one frequency band is utilized in one country. However, in many countries two or more frequency bands may be utilized depending upon the number of frequency bands that are available. For example, only the DCS-1800 (GSM-1800) band is used in Costa Rica while the GSM-850, GSM-900 and GSM-1900 bands are used in Guatemala and El Salvador. Although, Table 1 shows the different frequency bands for GSM systems, similar frequency bands are available for CDMA (Code Division Multiple Access) systems.
FIGS. 1 and 2 depict coverage areas of networks employing two frequency bands.
In FIG. 1, a first communication area 110 is an oval-shaped coverage area of a network employing a first frequency band (for example, GSM-850). A single base station does not have to cover the entire first communication area 110 for user equipments (e.g., cellular telephones, or other similar wireless communication devices). The first communication area 110 may be composed of coverage areas 117a, 117b, 117c and 117d associated with corresponding base stations 115a, 115b, 115c and 115d supporting the first frequency band. The coverage areas 117a, 117b, 117c and 117d may overlap with each other.
In the description, a communication area, e.g., the first communication area 110 refers to an area that is composed of coverage areas of multiple base stations supporting the same frequency band and enabling user equipments to communicate within the area or within other areas.
A second communication area 120 is an oval-shaped coverage area of a network employing a second frequency band (for example, GSM-1900). The second communication area 120 may be composed of coverage areas of multiple base stations (not shown) supporting the second frequency band in a manner similar to that described with regard to coverage area 110.
In the first communication area 110, user equipment may communicate with a base station or user equipment utilizing the first frequency band. In the second communication area 120, a user equipment may communicate with a base station or another user equipment utilizing the second frequency band. Hence, in the overlapping area 130 where the first communication area 110 overlaps with the second communication area 120, a user equipment may communicate with a base station or another user equipment utilizing either the first frequency band and second frequency band.
In an area that belongs to the first communication area 110 and does not belong to the second communication area 120, a user equipment supporting only the second frequency band may not communicate with a base station. In an area that belongs to the second communication area 120 and not the first communication area 110, a user equipment supporting only the first frequency band may not communicate with a base station.
A user equipment supporting two or more frequency bands are supplied in countries (or regions) employing two or more frequency bands for country-wide use. With a user equipment supporting two or more frequency bands, the user may communicate with a base station or another user equipment throughout the whole country while located in either the first communication area 110 or the second communication area 120.
However, compared with a user equipment supporting one frequency band, a user equipment supporting two or more frequency bands may require higher current consumption for performing a cell search.